The present invention relates, in general, to measuring film characteristics, and more particularly to simultaneously measuring thickness and composition of a lattice mismatched film on a semiconductor wafer.
Fabrication of many semiconductor devices requires the formation of a thin film on a semiconductor wafer, the thin film having a tightly controlled composition and thickness. According to the prior art, film composition was measured by methods such as secondary ion mass spectroscopy (SIMS), Rutherford backscattering spectroscopy (RBS) or Auger electron spectroscopy (AES). Film thickness was measured separately using transmission electron microscopy (TEM). The SIMS, RBS, AES and TEM methods require the use of equipment costing $2,000,000 to $3,000,000. These methods take over 20 hours for the two measurements and destroys the sample during the measurement process.
Ellipsometry is a method which uses polarized light to measure film thickness. Ellipsometry is economical, fast and does not damage the sample. According to the prior art however, a separate measurement using SIMS, RBS, or AES would still be required to measure film composition. As a result, typically one measurement was performed using SIMS, RBS, or AES to determine film composition and a second measurement was performed using TEM to determine film thickness. Details of these measurement methods as applied to films on semiconductor wafers are found in "SEMICONDUCTOR MATERIAL AND DEVICE CHARACTERIZATION" by D. K. Schroder, published in 1990 by John Wiley and Sons, Inc., which is incorporated herein by reference.
There is a need for a film measurement method which can be used for process control in a semiconductor manufacturing process. The method must not destroy or damage the workpiece and must be performed rapidly with a minimum of time and expense. Measuring both composition and thickness simultaneously is particularly desirable since the potential for error is reduced as well as further reducing the total measurement time.